This invention relates to medical systems and techniques for occluding aneurysms with an implanted embolic element. More particularly, an exemplary system provides a novel class of continuous extruded polymer embolic elements that carry a thin metallic surface layer to provide the embolic element with a specified resistance to electrical current flow. The system further provides an electrical source and controller (i) that modulates power delivery to the metallic component within a first (low) power range to cause a pre-selected thickness of coagulum to form about the embolic element to controllably increase the volume of occlusive material in an aneurysm; and (ii) that modulates power delivery in a second (high) power range to cause the metallic component to function as a fuse point exactly at the distal catheter termination to divide the deployed embolic element from the remainder of the continuous extrusion still in the catheter sleeve, thus allowing the physician to intra-operatively select any desired length of the embolic element for implantation.
Various devices and techniques have been developed for occluding aneurysms or other vascular defects or deformations (herein termed malformations). A common type of aneurysm treatment utilizes a detachable coil that is fed into the aneurysm to substantially occupy the aneurysm volume. The typical approach for implanting an embolic coil in an aneurysm involves attaching the coil to the distal end of a pushwire, and introducing the pushwire and coil through a catheter lumen until the coil is pushed into the aneurysm. The typical manner of detaching the coil from the pushwire involves using a direct current to cause electrolysis of a sacrificial joint between the pushwire and the coil. The coil can then serve to mechanically occlude a significant volume of the aneurysm and thereby reduce blood circulation within the aneurysm. After a period of time ranging from several hours to several weeks, the volume of the aneurysm can become fully occluded as blood clots about the coil. Eventually, the aneurysm will be reduced and reabsorbed by the body""s natural wound healing process. This type of vaso-occlusion system was disclosed by Gugliemli in U.S. Pat. Nos. 5,122,136 and 5,354,295.
Another manner of treating an aneurysm was disclosed by Gugliemli (see U.S. Pat. Nos. 5,976,131; 5,851,206). and is described as electrothrombosis. In this particular approach, a catheter and pushwire are used to push a wire coil into the aneurysm that is connected to an electrical source. The system then delivers radiofrequency (Rf) current to the coil which is adapted to heat the blood volume within the aneurysm to cause thermal formation of thrombus (see U.S. Pat. No. 5,851,206; Col. 5, line 5). The conductive coil disclosed by Guglielmi in U.S. Pat. No. 5,976,131 has an insulated tip or other arrangements of insulation around the coil to prevent localized xe2x80x9chot spotsxe2x80x9d (see U.S. Pat. No. 5,976,131; Col. 3, line 53).
It is believed that several risk factors are involved in any uncontrolled use of significant levels of Rf energy to cause so-called electrothrombosis. Most important, the use of electrical energy to cause current flow between a coil (first electrode) within an aneurysm and a ground (a second body electrode) will likely cause high energy densities and highly localized heating of tissue that comes into contact with the coil. If the wall of the aneurysm contacts the energized portion of a coil, there is a significant danger of perforation or ablation of the aneurysm wall that could be life-threatening. Further, the use of uncontrolled energy delivery to an implanted coil could heat adjacent brain tissue to excessive levels resulting in loss of brain function or even death. For these reasons, the coils disclosed by Gugliemli were provided with an insulating material covering the tip of the coil that is most likely to come into contact the wall of the aneurysm. However, it is still likely that unwanted localized heating will occur within the aneurysm sac when attempting to cause ohmic heating of the blood volume in an aneurysm by creating Rf current flow between an electrode coil and a body electrode.
Another disadvantage of using the typical commercially available wire coil is that the physician must estimate dimensions and volume of the aneurysm and then feed multiple coils into the aneurysm. The deployment of each coil is time consuming, and the detachment of the coil from the introducer pushwire also is time consuming.
In general, this invention comprises a vascular occlusion system for treating aneurysms that provides a novel class of continuous extruded polymer embolic elements that carry thin metallic or conductive coatings that provide a specified resistivity to electrical current flow. Alternatively, the polymer element is fabricated with such specified resistivity by providing conductive microfilaments or conductive particles embedded within an extruded polymer element. The embolic element is introduced into a targeted site in a patient""s vasculature by a microcatheter sleeve. The thin metallic coating allows the embolic element to be soft and flexible, and more importantly, allows the physician to select any desired length (and volume) of embolic element in vivo for causing mechanical occlusion of the aneurysm. The system of the invention also provides an electrical source and computer controller for feedback modulation of power delivery with a first (low) range and a second (high) range to accomplish two different methods of the invention. The electrical source is coupled to an electrode arrangement at the distal terminus of the catheter sleeve that contacts the surface of the embolic element as it is slidably deployed from the catheter. Thus, energy is delivered to the resistive layer of the embolic element directly from the distal terminus of the catheter sleeve. The catheter working end also carries a thermocouple, coupled to feedback circuitry, for sensing the temperature of the deployed embolic element and controlling its temperature via power modulation. The embolic element can be fabricated with a resistive metallic component to cooperate with single electrode have a single polarity at the catheter working end. Alternatively, the embolic element can be fabricated with spaced apart metallic surface portions to cooperate with bi-polar electrodes at the catheter working end.
In a method of using an exemplary system, the physician pushes the embolic element from the distal terminus of a catheter into a targeted site in a patient""s vasculature thereby mechanically occluding a selected volume of the aneurysm or other vascular malformation. After disposing a selected length of the embolic element within the targeted site, the physician then actuates the electrical source via the controller to deliver electrical current within a first (low) power range to the conductive component of the polymer element from the electrode at the catheter""s distal terminus. The electrical energy delivery to the metallic component that provides the specified resistivity (e.g., preferably ranging between about 0.5 ohms and 25 ohms/cm. of embolic element) causes resistive heating of the surface of the deployed embolic element over a particular calculated length of the element that extends distally from the electrode. This thermal effect causes denaturation of blood components that results in the formation of layer of coagulum about the deployed embolic element. Additionally, the current flow within this first range causes active or ohmic heating of blood proximate to the embolic element in a manner that facilitates the formation of the coagulative layer about the embolic element. During energy delivery, the temperature sensor at the catheter working end sends signals to the controller that are used to modulate power delivery to maintain the embolic element at, or within, a particular temperature or range at the catheter""s distal terminus. By this manner of operation, the system can controllably create a selected thickness of coagulum about the surface of the embolic element. Thus, the initial deployment of the selected length of the embolic element mechanically occludes or occupies a selected (first) volume of a vascular malformation. Thereafter, controlled energy delivery thermally induces a layer of coagulative to form, thereby providing another selected volume of material to occlude or occupy a selected (second) volume of the vascular malformation. These methods of the invention provide means to cause rapid mechanical occlusion of blood flow within the malformation while preventing any significant energy densities in the targeted site.
In the next manner of practicing a method of the invention, the physician directs the controller and electrical source to deliver current at a second (higher) power level to the metallic component of the embolic element from the same electrode arrangement at the catheter""s distal end. This second power level causes the metallic component together with the polymer core of the embolic element to act like a fuse at the catheter sleeve""s terminus. This selected power level, within a fraction of a second, can thermally melt or divide the deployed portion of the continuous polymer embolic element from the remainder of the element still within the catheter sleeve. This aspect of the method of the invention allows the physician to select any length of embolic element intra-operatively under fluoroscopy, which is not possible in the prior art.
The invention advantageously provides a system and method for intra-operatively disposing any selected length and selected volume of an occlusive element in a targeted site in a patient""s vasculature to mechanically occlude a malformation.
The invention provides a system and method that does not require the physician to pre-select a particular length of a coil element for implantation in an aneurysm.
The invention provides a system and method that does not require the physician to deploy multiple separate coil elements in separate sub-procedures to occlude an aneurysm.
The invention advantageously provides a system and method that utilizes a polymer embolic member that carries a metallic component with a specified resistivity to current flow to thereby allow controlled energy delivery within, and about, the member to create a pre-determined thickness of coagulum about the embolic member for mechanically occluding a vascular malformation.
The invention provides a system with feedback control that modulates power delivery from a source to an embolic element to maintain the embolic element at a specified temperature or within a specified temperature range.
The invention provides a system with feedback control that modulates power delivery to create a pre-selected thickness and volume of occlusive material about an embolic element.
The invention provides a self-terminating electrical energy delivery modality for creating a layer of occlusive material about an embolic element.
The invention advantageously provides a system and method that allows the delivery of electrical energy to an embolic element within an aneurysm without the risk of localized high energy densities.
The invention advantageously provides a system and method that delivers electrical energy to an embolic element to increase the volume of occlusive material in an aneurysm while eliminating the risk of perforating the wall of the aneurysm.
The invention provides a system and method that delivers electrical energy to an embolic element to increase the volume of occlusive material in a cerebral aneurysm while preventing collateral thermal damage to brain structure.
The invention provides an embolic member with a specified resistivity by fabricating the a polymer member with at least one very thin conductive surface layer.
The invention provides an embolic member with a specified resistivity by fabricating the polymer extrusion with conductive microfilaments embedded therein.
The invention provides an embolic member with a specified resistivity by extruding a polymer matrix with conductive particles embedded therein.
The invention advantageously provides a system and method utilizes a polymeric element with first and second portions of a metallic cladding that is adapted to serve as a bi-polar electrode arrangement for creating a coagulative layer.
The invention provides a method for controllably creating a coagulative volume about an embolic member by (i) controlling the center-to-center distance between spaced apart conductive components of the embolic member, and (ii) controlling the rate of energy delivery between the spaced apart conductive portions.